Expanded olefin polymer

Abstract

A thermoplastic synthetic resin such as polyethylene or ethylene-vinyl acetate copolymer resin containing 0.1 to 10 wt. % of a specific additive selected from specific classes of compounds, namely saturated higher fatty acid amides, saturated higher aliphatic amines and complete esters of saturated higher fatty acids is found to be very suitable for production of expanded articles and can be easily formed into expanded articles with little shrinkage after expansion, free from creases on the surface or cracks on the cell walls, and having excellent characteristics such as good closed cellular characteristic, higher compressive strength, low density, etc.

What we claim is: 
     
       1. An expanded article of an olefin polymer comprising an expanded product of an olefin polymer containing at least one compound, which imports little shrinkage to said expanded article after expansion selected from the group consisting of the compounds represented by the formulas (I), (II) and (III) as set forth below in an amount of 0.1 to 10% by weight based on the weight of said resin and having a closed cellular characteristic value of 0 to 0.5 g/cm 3 , a bulk density of 10 to 200 kg/m 3  and a compressive strength coefficient of 2.15×10 -3  to 2.89×10 -2  : ##STR8## wherein R 1  is an alkyl group having 10 to 24 carbon atoms, X and X' each hydrogen atom, an alkyl group having 1 to 24 carbon atoms which may be substituted or a substituent selected from the group consisting of --(CH 2 ) n  NH 2  wherein n is an integer of 1 to 22, ##STR9## wherein R 5  is an alkyl having 1 to 24 carbon atoms, --(R 4  O) m  H wherein R 4  is an alkylene group having 1 to 5 carbon atoms and m an integer of 1 to 10, ##STR10## wherein R 5  is an alkyl having 1 to 24 carbon atoms, ##STR11## wherein n is an integer of 1 to 22 and A is hydrogen atom or ##STR12## wherein A' is hydrogen atom or ##STR13## wherein R 2  is an alkyl group having 9 to 23 carbon atoms, Y and Y' each hydrogen atom, an alkyl having 1 to 24 carbon atoms, an acyl having 10 to 24 carbon atoms or a substituent of the formula --(R 4  O) m  A 2  wherein A 2  is hydrogen atom, an alkyl having 1 to 24 carbon atoms or acyl having 10 to 24 carbon atoms; ##STR14## wherein means plural alkyl or hydroxyalkyl groups corresponding in number to the integer l, which may be the same or different, each having 9 to 23 carbon atoms, R 4  an alkylene group having 1 to 5 carbon atoms, k an integer of 0 to 7, l an integer of 2 to 8 and Z a l-valent residue of l-valent polyhydric alcohol from which l hydroxyl groups are eliminated. 
     
     
       2. An expanded article according to claim 1, wherein the polyolefin resin is a olefin polymer or an ethylenevinyl acetate copolymer resin. 
     
     
       3. A process for expanding an olefin polymer, which comprises incorporating at least one compound, which imparts little shrinkage to said expanded polymer after expansion, selected from the group consisting of the compounds of the formulas (I), (II) and (III) as set forth below in a thermoplastic synthetic resin in an amount of 0.1 to 10% by weight based on the weight of said resin together with a blowing agent under the condition maintained at a temperature in the range from about 15° to 300° C. to form an expandable resin composition and then allowing said resin composition to expand utilizing the expanding force of the blowing agent contained therein: ##STR15## wherein R 1  is an alkyl group having 10 to 24 carbon atoms, X and X' each hydrogen atom, an alkyl group having 1 to 24 carbon atoms which may be substituted or a substituent selected from the group consisting of --(CH 2 ) n  NH 2  wherein n is an integer of 1 to 22, ##STR16## wherein R 5  is an alkyl having 1 to 24 carbon atoms, --(R 4  O) m  H wherein R 4  is an alkylene group having 1 to 5 carbon atoms and m is an integer of 1 to 10, ##STR17## wherein R 5  is an alkyl having 1 to 24 carbon atoms, ##STR18## wherein n is an integer of 1 to 22 and A is hydrogen atom or ##STR19## wherein A' is hydrogen atom or ##STR20## wherein R 2  is an alkyl group having 9 to 23 carbon atoms, Y and Y' each hydrogen atom, an alkyl having 1 to 24 carbon atoms, an acyl having 10 to 24 carbon atoms or a substituent of the formula --(R 4  O) m  A 2  wherein A 2  is hydrogen atom, an alkyl having 1 to 24 carbon atoms or acyl having 10 to 24 carbon atoms; ##STR21## wherein means plural alkyl or hydroxyalkyl groups corresponding in number to the integer l, which may be the same or different, each having 9 to 23 carbon atoms, R 4  an aklylene group having 1 to 5 carbon atoms, k an integer of 0 to 7, l an integer of 2 to 8 and Z a l-valent residue of l-valent polyhydric alcohol from which l hydroxyl groups are eliminated. 
     
     
       4. A process according to claim 3, wherein the olefin polymer is cross-linked. 
     
     
       5. A process according to claim 3, wherein the olefin polymer is a polyethylene resin, an ethylene-vinyl acetate copolymer resin, or a polypropylene resin. 
     
     
       6. A process according to any of claims 3 to 5, wherein the polymer composition is expanded by extrusion foaming by means of an extruder.